# 104. Maximum Depth of Binary Tree

[Link](https://leetcode.com/problems/maximum-depth-of-binary-tree/)

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

**Note:** A leaf is a node with no children.

**Example:**

Given binary tree `[3,9,20,null,null,15,7]`,

```
    3
   / \
  9  20
    /  \
   15   7
```

return its depth = 3.

**Solution**

這題概念跟上一題一樣

```
    public int maxDepth(TreeNode root) {
        if(root == null) return 0;
        int left = maxDepth(root.left);
        int right = maxDepth(root.right);
        int depth = 0;
        if(left == 0 && right != 0) depth = right + 1;
        else if(left != 0 && right == 0) depth = left + 1;
        else if(left != 0 && right != 0) depth = Math.max(left, right) + 1;
        else depth = 1; //left == 0, right == 0
        return depth;
    }
```
